The present invention relates in general to a biomagnetic field measuring apparatus using SQUID (Superconducting Quantum Interference Device) magnetometers for measuring a weak magnetic field generated from the heart, the brain or the like of an adult, a child, an unborn baby or a fetus, or the like. In particular, the invention relates to a method of evaluating the rotational property of a current in the heart or the brain on the basis of the distribution of the measured magnetoencephalogram and the measured magnetocardiogram.
Heretofore, a biomagnetic field measuring apparatus employing SQUID magnetometers has been used in the measurement of a weak biomagnetic field (the measured magnetic field is called the magnetocardiogram or the magnetoencephalogram) which is caused by an ion current generated along with the myocardial electric activity within an organism (generality of the muscle activity) or the activity of neurons in the brain. The motion of the ion current reflects the electric activity of an organism. Thus, the useful information can be obtained from the motion of an ion current and hence many studies are being made. As a method of observing a pseudo-current within the heart from these measured magnetic fields, the current-arrow map method has been proposed (Medical and Biological Engineering and Computing 2001, Vol. 39, pp. 21-28). The calculation for the current-arrow map method is obtained by differentiating partially the magnetic field in a normal component (i.e., the magnetic field in a direction intersecting perpendicularly an organism) with respect a tangential component (i.e., a direction parallel with an organism). Thus, the pseudo-current in the inside of the heart can be estimated by utilizing the current-arrow map method, and thus the effectiveness of the current-arrow map method has been shown.
However, the method of evaluating quantitatively a rotating current within the brain or the heart is not considered, and hence it is impossible to obtain the information which can be sufficiently clinically evaluated.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problem associated with the prior art, and it is therefore an object of the present invention to provide a method of evaluating quantitatively the rotational property of a current within the brain or the heart on the basis of the magnetic field waveform which is obtained by using a biomagnetic field measuring apparatus for measuring a weak magnetic field generated from the brain or the heart.
In order to attain the above-mentioned object, according to the present invention, there is provided a biomagnetic field measuring apparatus including: a plurality of magnetometers each employing a superconducting quantum interference device (hereinafter, referred to as an SQUID for short, when applicable) for measuring a magnetic field generated from an organism; a unit for calculating a pseudo-current on the basis of the measured magnetic field; a unit for calculating the pseudo-current on the basis of the magnetic field obtained by the plurality of magnetometers to integrate the pseudo-current in a fixed direction on a circumference which is a fixed distance away from each of the sensors; a unit for calculating a maximum value or a minimum value of the integral value obtained by the unit for carrying out the integration; and a unit for calculating a difference value between the absolute value of the maximum value and the absolute value of the minimum value.
According to the present invention having the above-mentioned construction, it is possible to obtain easily the information useful in the quantitative evaluation of the rotational property on the basis of the magnetic field distribution having the rotating current in patients with dizziness, patients with atrial flutter or the like.
As described above, according to the present invention having the above-mentioned construction, it is possible to obtain an index useful in the diagnosis.